1. Field of the Invention
The present invention relates to an optical information recording medium, and more particularly to a phase-change optical information recording medium in which information is recorded, reproduced and rewritten by changing an optical property of a material in the phase-change recording layer thereof by irradiating the recording layer with a light beam.
2. Discussion of the Related Art
Japanese Patent No. 02652443 (i.e., Japanese Laid-Open Patent Publication No. 1-220126, hereinafter JPxe2x80x2 443) discloses a method for recording information, such as address information for EFM signals with respect to CD-RW, in an information carrier 11 as shown in FIG. 6A. In addition, JPxe2x80x2 443 discloses a method in which a wobbling groove is used to input address information with respect to DVD. FIGS. 6C and 6D are enlarged views of a portion 12 of the information carrier 11 shown in FIG. 6A, and FIG. 6B is a cross-section of the information carrier 11 when the carrier is cut at a line bxe2x80x94b shown in FIG. 6A. As shown in FIG. 6B, the information carrier 11 has a sinusoidally wobbling servo track 14. In FIG. 6B, numerals 15, 16 and 17 denote a transparent substrate, a recording layer and a protective layer, respectively. It is described in JPxe2x80x2 443 that the servo track 14 has a frequency component which is produced by track modulation and which has an average frequency of 22.05 KHz, and that the frequency of the track modulation is modulated according to position information signals. However, information to be input in the information carrier has to satisfy the respective specified conditions for each application, and therefore when a disk is manufactured, the groove and recording layer have to be optimized so as to be suited for the application. The recording medium of the present invention satisfies the disk standards of 4.7 GB DVD+RW. An optical information recording medium satisfying the standards has not yet been disclosed.
Recently, rewritable optical disks which have the same capacity as high density DVD-ROMs and in which information can be recorded at the same speed as that for high density DVD-ROMs. These rewritable optical disks typically have a wobbling guide groove in their substrate to read and write information therein, and information such as clock information and address information of signals is input in the guide groove.
Because of these reasons, a need exists for a rewritable optical information recording medium which has the same capacity as high density DVD-ROMs and good recording properties even when information is recorded at a high speed.
Accordingly, an object of the present invention is to provide a rewritable optical information recording medium which has the same capacity as high density DVD-ROMs and good recording properties even when information is recorded at a high speed.
To achieve such an object, the present invention contemplates the provision of a phase-change optical information recording medium in which information is recorded, reproduced and rewritten by changing an optical property of a material in the phase-change recording layer thereof by irradiating the recording layer with a light beam and which includes a first transparent substrate (such as polycarbonate plates) having a wobbling groove which is spirally formed thereon at a pitch; a first dielectric layer located overlying the first transparent substrate and having an optical thickness nd (i.e., refractive index (n)xc3x97thickness (d)) of from 80 nm to 200 nm; a phase-change recording layer located overlying the first dielectric layer and having an optical thickness of from 20 nm to 50 nm (preferably 30 nm to 50 nm) when the recording layer is in an erased state; a second dielectric layer located overlying the recording layer and having an optical thickness of from 10 nm to 70 nm; a reflection layer including a metal; and a second transparent substrate (such as polycarbonate plates) located overlying the reflection layer.
The first and second transparent substrates preferably have the same thickness.
A third dielectric layer may be formed between the second dielectric layer and the reflection layer. A weather resistance layer may be formed between the reflection layer and the second transparent substrate. In addition, an adhesive layer may be formed between the second transparent substrate and the reflection layer (or the weather resistance layer).
The refractive index (n) and thickness (d) of the first transparent substrate having a wobbling groove are preferably from 1.50 to 1.65 and from 0.59 mm to 0.62 mm, respectively.
In addition the first transparent substrate preferably has an absolute value of birefringence not greater than 50 nm.
The pitch of the wobbling groove is preferably from 0.70 xcexcm to 0.80 xcexcm. It is preferable that the wobbling groove has an amplitude of from 15 nm to 40 nm and clock information is input in the wobbling groove using a first sinusoidal wobble having a first phase and address information and disk information are input in the wobbling groove using a second sinusoidal wobble having a phase different from the first phase by 180xc2x0.
It is preferable that the wobbling period, depth and width of the wobbling groove is from 0.40 xcexcm to 0.45 xcexcm, from 22 nm to 40 nm and from 0.17 xcexcm to 0.30 xcexcm, respectively.
It is preferable that recording marks are recorded in the groove, wherein the width of the recording marks is from 0.9 to 1.5 times the width of the wobbling groove.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.